The recent deregulation of the utility industry has created a market for products that facilitate the efficient distribution and monitoring of electrical power. In the past, utilities have built systems that did not provide certain information that is considered necessary to adequately monitor the electrical energy that is provided to and from a substation, or multiple substations, and related feeder networks and the like. For example, existing metering systems have been used to monitor the phase voltage or phase current for each phase of a multiphase utility service system to determine whether it is within an absolute limit (i.e., between an upper and a lower threshold). Predetermined actions, such as activating an alarm or a warning, are taken when a threshold is crossed. However, such monitoring does not identify situations where the phase voltages or currents are within individual phase limits but are not proportional to each other. In other words, the phase voltages/currents are not checked relative to each other. Therefore, there can be some imbalance, although each phase is within its absolute limit.
Imbalance can exist, for example, when two phases are at the top of their current or voltage range, and one is at the bottom of its range. For example, phases A and B may be at 110% of their nominal values, and phase C may be at 90% of its nominal value. Each phase may be within individual phase limits, but the voltages/currents supplied by each phase are not equal (e.g., there may be a problem with phase C). Imbalance is not desirable, and in many applications, it is desirable to maintain closely balanced phase voltages and phase currents. Thus, in prior art systems, there is no indication of a phase voltage or phase current problem as long as each phase is within its predetermined limits, although imbalance may exist.
One reason to monitor voltage and/or current imbalance is economic, e.g., imbalance will affect equipment and processes and can result in misoperation and damage of equipment, disruption of operations, and other such anomalies. Moreover, imbalance is prohibited within some systems (e.g., imbalance determination is mandatory in some countries, such as India). Furthermore, a consumer, such as a business, may now be able to choose its utility provider, and therefore the customer may now have a need or desire to determine the quality of the power supplied by its present supplier. Similarly, the utilities have a need to monitor the power they supply to customers to ensure that they are providing power that is sufficiently balanced to retain their customers. Therefore, utilities and consumers are now in need of a metering system to detect voltage and current imbalance.
Although the art of metering systems is well developed, there remain some problems inherent in this technology, particularly the ability to detect voltage and current imbalance in multiphase service. Therefore, a need exists for a system and method for detecting imbalance that overcomes the drawbacks of the prior art.